This proposal requests funding for a gas chromatograph-mass spectrometer. Expansion of the user community in the Department of Chemistry at the University of California, Irvine, through recruitment of senior and junior faculty and a the development of research projects in which there are specific requirements for both increased sample capacity and real-time answers demonstrate the urgent need for this instrumentation to obtain vital analytical data that cannot be obtained by other techniques. The UCI mass spectrometry facility which comprises of two magnetic sector instruments is fully saturated providing analytical support for synthetic program (exact mass determinations) and other problem solving, particularly using LSIMS, direct probe and FD. Research projects of the major users include: (a) SHEA, (b) Overman- discovery of new reactions and strategies and the synthesis of complex molecules, particularly through multiple stereospecific ring formation, (c) Rychnovsky- structure determination and convergent synthesis of polyene macrolide antibiotics, chiral nitroxides as enantioselective oxidation catalysts; (d) Van Vranken-dearomatization reactions in chemical systems investigated via the aromatic [2,3]-Witting reaction and asymmetric versions of the Sommelet-Hauser and thia-Sommelet reaction using 2,6-disubstituted aromatics; (e) Woerpel-stereospecific synthesis particularly involving insertions into silacyclopropanes, rearrangements of alpha-alkoxyallylsilanes, lithium enolate chemistry and palladium catalyzed coupling reactions. Aside from the major user group there are may other NIH funded research groups who urgently require GC-MS capability. The instrumentation is to be equipped for EI and CI, both of which are essential for obtaining structural information. In addition, by using an autosampler and appropriate computing capacity the instrument will be formatted for a limited number of graduate student users and will, therefore, be able to provide the type of turn around that is needed while leaving the instrument under the control of experienced mass spectroscopists, the facility director has over 20 years experience much of it utilizing GC-MS. UCI has a long-term major funding commitment to the mass spectrometry facility as well as the other analytical spectroscopy instrumentation facilities which support the research faculty. Currently the annual commitment is almost 500,000 dollars to these facilities in salaries and operational support. Additional operational funding is obtained though charges to the grants and contracts of the user community.